X-ray radiography systems are used for diagnostic imaging, whereby they provide image data of a region of a patient's body to be examined in order to make possible or to simplify a medical diagnosis. The image data is obtained with the aid of an x-ray source and an x-ray-sensitive x-ray detector. A modern digital x-ray system is described in U.S. Pat. No. 6,733,176 for example.
A problem with x-ray imaging is that the image quality is adversely affected by what is known as radiation scatter. Radiation scatter occurs when x-ray radiation not only strikes the x-ray detector on a direct path from the x-ray focus through the object under examination but is also scattered in the object under examination. The scattered radiation frequently overlays the actual x-ray image and with specific images can account for up to 80% of the detected radiation. The scattered radiation is routinely reduced by what is known as an anti-scatter grid. In the simplest case this involves a plate disposed in front of the x-ray detector with x-ray-absorbing septa which are aligned to the x-ray detector and which filter out the scattered radiation. Anti-scatter grids have the problem however that on the one hand they still let through part of the scattered radiation and on the other hand they also absorb a significant part of the direct x-ray radiation (up to 50%). This additionally increases the exposure of a patient to x-rays.
Another way of reducing the scattered radiation is what is known as slot scanning. In such cases a slot-shaped x-ray beam is generated which is moved by movable collimators over the entire imaging area. On the detector side only the narrow area is screened out by a further collimator so that the scattered radiation can be very greatly reduced. An x-ray imaging system with a scanning tube is described in U.S. Pat. No. 4,803,714 for example.
Despite greatly improving radiation scatter, slot scanning systems have as yet not become established. The main reason for this is the high outlay for the mechanical movement of tube-side collimator and detector-side collimator. A new approach for flat panel detectors is described in Liu et. al: “An Alternate Line Erasure and Readout (ALER) Method for Implementing Slot-Scan Imaging Technique With a Flat-Panel Detector—Initial Experiences”, IEEE Trans. Med. Imaging 2006, April 25(4), pp. 496-502. This system uses an “electronic collimation” on the detector side, with the detector lines not directly irradiated being discarded. However this system still needs a mechanically-movable tube-side collimator.